Fastrak as used for more than just paying tolls
I recently bought a transponder tag for my car. It's registered with the state and is associated with my license plate. If I drive through a toll facility which is suitably equipped, it will automatically subtract from my balance. When the balance drops too low, it will replenish itself by applying a charge to my usual payment instrument.
In the Bay Area, this mostly applies to bridges, but there are also a couple of freeways which have "express lanes" -- lanes where it's free if you're a carpool, but you have to pay otherwise during rush hour. Having the transponder mounted on your windshield so it can be read is how you pay for using those lanes if you're a solo driver. If you're carpooling, you're supposed to remove it and put it in a little anti-static bag they supply.
There is at least one other use for these transponders: traffic speed detection. Some freeway segments have the equipment needed to read the tags as they pass underneath. If the same ID appears at two known places a known distance apart in a known amount of time, then calculating the speed is a simple matter. This isn't particularly surprising or even new. It's been done in a bunch of places for years. In San Antonio, the state gave away a whole bunch of these things just so they'd have more roaming data points on the roads.
For a while, I had a transponder tag for a parking garage on my car. It was made by the same company who made the tags the state was giving out. I imagine that every time I drove under one of their readers, it picked up on the ID and made a note of it. The next time I passed another reader, it did the math and figured out a speed for that road segment.
Rejoining the world of tagged vehicles got me thinking about other potential uses for this technology. Mostly, I started thinking about how to stop criminals with it. Imagine what would happen if most cars on the road had some kind of unique identifier which could be interrogated at a distance. It would open up a whole bunch of possibilities.
First, realize that probably every car already has a unique ID: the VIN. You have to get up close and personal to actually read it, though. If the vehicle is in motion or you otherwise can't get right up to the windshield, you probably can't read it. There are license plates, but those can be hard to copy down on the fly, and they can be removed or changed.
So let's say this exists, and most cars have a transponder tag which has been added on, or some equivalent device which is part of the built-in electronics. Now let's say a car is involved in some kind of crime. As long as there was some kind of listening device which logged it in the vicinity of the crime at the right time, it can probably be found later.
What's going to do that sort of logging? Easy: other cars. I imagine a "smart grid" situation in which cars talk to each other and the road itself. There are already city transit agencies starting to get licenses for this kind of technology. The magic terms are "5.9 GHz DSRC". Look it up - it's fascinating stuff.
Is it such a stretch to think that cars are going to start noticing each other? I don't think so. Airplanes are already headed in that direction with ADS-B. One interesting point about the ADS-B system is how aircraft learn about each other and share that data with others. If I'm reading this correctly, plane A can see plane B and tell plane C about it. C couldn't see B directly,, but knows of its existence thanks to the report from A. This even applies if C is using a receive-only "in" system.
It's definitely not a stretch to imagine cars being scanned on purpose after a crime happens. Police agencies already drive their "PIPS" cars through an area where something has occurred. This way, if the bad guys left their car in the area and later come back to it, there's a log of it being there. If that same car shows up at yet another crime site later, it can be correlated.
I've seen my local PD driving up and down the lanes at the big movie theater parking lot to look for interesting cars. The cameras on top scan plates as they pass by, and the computer does the rest. They wind up recovering a bunch of stolen cars this way.
I'm not trying to make dire predictions of a "grim meathook future" or anything like that. It just seems likely that such technologies will be much more closely related not too long from now. It doesn't even really have to involve law enforcement or their federal buddies. The nerd contingent could get going on it right now for their own enjoyment. They're already doing it for ADS-B data with those $20 RTLSDR TV tuner sticks. (Really.)
Let's just hope this tech is used for the right reasons.